JP4018239B2 - Optical fiber preform manufacturing method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an optical fiber preform manufacturing method that stably supports an optical fiber preform when soot is deposited, dehydrated, made transparent, or drawn during an optical fiber manufacturing process.
[0002]
[Prior art]
As is well known, during the optical fiber manufacturing process, when soot is deposited, dehydrated, made transparent, or drawn, the optical fiber preform is placed in a porous body manufacturing chamber or a furnace core tube of a heating furnace, Since it is necessary to hang vertically in the direction and perform a desired operation, a rod-shaped rod is provided at the upper end portion of the optical fiber preform, and this is used as a hanging rod. The suspension rod may be an extension of the starting rod of the optical fiber preform, or may be a suspension-only dummy rod that is purposely connected to the upper end of the departure rod.
[0003]
In any case, conventionally, when performing the various operations described above, the suspension rod is held by the lower end of the support rod attached to the manufacturing apparatus side equipped with a rotation mechanism and a vertical movement mechanism. The optical fiber preform is supported.
[0004]
For gripping the suspension rod on the optical fiber preform side and the support rod on the manufacturing apparatus side, for example, methods as shown in FIGS. 5 to 7 have already been proposed.
5 to 7, a cylindrical portion 11 is provided at the lower end of the supporting rod 10 on the manufacturing apparatus side, and the cylindrical portion 11 has a through hole 12 for a locking pin that penetrates in the radial direction (horizontal direction). Is provided. On the other hand, on the upper end side of the suspension rod 21 on the side of the optical fiber preform 20 inserted into the cylindrical portion 11 of the support rod 10, the lock pin is similarly positioned at a position corresponding to the through hole 12 for the lock pin. Through-holes 22 are provided, the corresponding through-holes 12 and 22 on the cylindrical portion 11 side and the suspension rod 21 side are aligned and communicated, and the through-holes 12 and 22 communicated with each other are connected. A stop pin 30 is inserted to support the optical fiber preform 20.
[0005]
According to this support method, the upper end side of the suspension rod 21 on the optical fiber preform 20 side is inserted into the cylindrical portion 11 of the support rod 10, the through holes 12 and 22 are aligned, and the locking pin 30 is inserted. Therefore, there is an advantage that it is simple and the workability is good.
[0006]
[Problems to be solved by the invention]
However, in the conventional method described above, the upper end side of the suspension rod 21 on the optical fiber preform 20 side may be thermally deformed during various heating during the optical fiber manufacturing process. It was necessary to form the inner diameter (insertion opening) of the cylindrical portion 11 on the support rod 10 side somewhat larger than the diameter. For example, although depending on the outer diameter of the suspension rod 20, the diameter of the base material to be manufactured, and the like, the inner diameter of the cylindrical portion 11 on the support rod 10 side is 0.2-0. It is about 4 mm larger.
[0007]
That is, the suspension rod 21 on the optical fiber preform 20 side is not firmly inserted into the cylindrical portion 11 on the support rod 10 side and coupled, but is held in a rough shape with a certain margin.
[0008]
Under such a rough coupling state, when the supporting rod 10 is rotated by the manufacturing apparatus side in the various manufacturing processes, there is a possibility that the rotation on the optical fiber preform 20 side may also fluctuate. If there is such a fluctuation, there is a concern that soot deposition without eccentricity, uniform heating, and even drawing with uniform tension cannot be guaranteed, and this greatly affects the quality of the optical fiber obtained later. To give. In particular, in the soot deposition, since the total weight of the soot is small at the start, there is almost no shaking on the optical fiber preform 20 side, but the deposition tends to swing as the soot progresses and the outer diameter of the soot increases. Thus, since the base material weight may reach several kilograms at the end of the deposition, the optical fiber base material 20 side sometimes oscillates periodically.
[0009]
Actually, in the optical fiber obtained by using the optical fiber preform 20 manufactured by the above-described conventional method, the refractive index distribution structure of the cross section is not a uniform concentric shape but a non-circular shape having a slight deviation. There was to be. Such a bias causes a problem that polarization mode dispersion increases. In particular, in recent large-capacity, ultra-long-distance repeaterless transmission, when polarization mode dispersion increases, signal degradation accumulates, which is a further problem.
[0010]
Also, since polarization mode dispersion is greatly affected by the difference in relative refractive index, an optical fiber having a large relative refractive index difference, such as an erbium-doped optical fiber or a dispersion compensating optical fiber, has a non-circular shape as a base material. There was also a problem that the effect of.
[0011]
Therefore, the present inventor has eagerly studied about a method for stably holding the optical fiber preform in a simple operation by a simple operation. It has been found that good results can be obtained when the lower end of the optical fiber and the suspension rod on the optical fiber preform side are coupled.
[0012]
The present invention has been made from such a viewpoint, and it is intended to provide a method of manufacturing an optical fiber preform that is coupled and held by locking pins from a plurality of different directions. It is.
[0013]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a method for producing an optical fiber preform in which a suspension rod on the optical fiber preform side is held at the lower end of a support rod for the optical fiber preform to perform a desired process. In
A cylindrical portion is provided at the lower end of the supporting rod, and the cylindrical portion is penetrated for the locking pin at at least two positions that are appropriately spaced apart in the longitudinal direction and that have different radial directions. While the hole is provided, the upper end of the suspension rod on the optical fiber preform side inserted into the cylindrical portion of the support rod is also used for the lock pin at a position corresponding to the through hole for the lock pin. The through holes corresponding to each other on the cylindrical portion side and the suspension rod side are aligned and communicated, and a locking pin is inserted into each of the communicated through holes, and the optical fiber An optical fiber preform manufacturing method is characterized in that the preform is supported.
[0014]
According to the second aspect of the present invention, the interval between the through-holes of the cylindrical portion of the support rod and the suspension rod on the optical fiber preform side is at least twice the outer diameter of the suspension rod. The method of manufacturing an optical fiber preform according to claim 1.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
1 to 2 show an example of a gripping state between the lower end of the support rod and the suspension rod on the optical fiber preform side in the method of the present invention.
Also in the present invention, the manufacturing apparatus system to be used is basically the same as the conventional one. Therefore, the same or similar symbols are attached to the same components as those in FIGS. Among them, 10 is a supporting rod, 11 is a cylindrical portion at the lower end thereof, 21 is a hanging rod on the optical fiber preform side, and 30A to 30B are locking pins. Here, the inner diameter (insertion opening) of the cylindrical portion 11 at the lower end of the support rod 10 is made larger by about 0.2 to 0.4 mm than the outer diameter D of the suspension rod 21.
[0016]
First, in the present invention, the cylindrical portion 11 at the lower end of the support rod 10 is provided at two positions (90 ° different 2 positions) at positions that are appropriately separated in the longitudinal direction (axial direction) and in different radial directions. On the upper end side of the suspension rod 21 on the side of the optical fiber preform, positions corresponding to the through holes 12A to 12B for the locking pin (also: Similarly, through holes 22A to 22B for locking pins are provided at two positions whose radial directions differ by 90 °.
[0017]
In order to couple and hold the upper end side of the suspension rod 21 on the optical fiber preform side to the cylindrical portion 11 side of the lower end of the support rod 10, the suspension rod is suspended from below on the cylindrical portion 11 of the support rod 10. 21 is inserted, the corresponding through holes 12A to 12B and 22A to 22B on the cylindrical portion 11 side and the hanging rod 21 side are aligned and communicated with each other, and each of the communicated through holes 12A to 12A is connected. It is only necessary to insert the locking pins 30A to 30B into 12B and 22A to 22B, respectively.
[0018]
Then, as described above, even if the inner diameter of the cylindrical portion 11 at the lower end of the support rod 10 is larger than the outer diameter D of the suspension rod 21 on the optical fiber preform side, In the locking pin 30A, since the locking pin 30A is passed through the through-hole 12A in the same direction of the hanging rod 21, the shaking and backlash in the same direction can be effectively suppressed, while the front-rear direction is reduced. In the locking pin 30B, the locking pin 30B is penetrated through the through-hole 12B in the same direction of the suspension rod 21, so that the shaking and backlash in the same direction are effectively suppressed.
[0019]
That is, the locking pins 30A to 30B from two different directions restrict the swinging and backlash of the suspension rod 21 on the optical fiber preform side from the front and rear, left and right two-dimensional directions. It is stably and vertically gripped with high accuracy. Of course, this effectively prevents fluctuations during rotation of the optical fiber preform.
[0020]
On the other hand, if only the locking pin 30A in the left-right direction is used, the suspension rod 21 on the optical fiber preform side may swing in the front-rear direction in the figure with the locking pin 30A as a fulcrum. In the case where only the locking pin 30B in the front-rear direction is used, the suspension rod 21 on the optical fiber preform side may swing in the left-right direction in the figure with the locking pin 30B as a fulcrum. It turns out that it is enough.
[0021]
Furthermore, in the present invention, as described above, in the cylindrical portion 11 of the support rod 10 and the suspension rod 21 on the optical fiber preform side, the lower through holes 12A and 22A and the upper through holes 12B and 22B In the meantime, an appropriate separation distance L is provided in the longitudinal direction, and the two fulcrum points by the respective locking pins 30A to 30B inserted into the communicating through holes 12A to 12B and 22A to 22B are considerably separated. I try to take it.
[0022]
If these two fulcrums are separated, the optical fiber preform suspended from the lower end side of the suspension rod 21 is quite long and has a large weight. As compared with the case where the two are close to each other, a large resistance force is obtained, and as a result, it is possible to more effectively prevent the optical fiber preform side and, hence, the suspension rod 21 from shaking.
[0023]
And, as will be described later, the separation distance between both fulcrums, that is, the separation distance L between the upper and lower through-holes, according to the experiments conducted by the present inventors, is relative to the suspension rod 21 on the optical fiber preform side. It has been found that a better anti-sway effect can be obtained by setting the outer diameter D to be twice or more.
[0024]
Further, in the same member of the cylindrical portion 11 of the support rod 10 and the suspension rod 21 on the side of the optical fiber preform, the upper and lower through holes are formed in such a shape that is spaced apart from each other by the above-described vibration L. In addition to the stopping effect, it is possible to effectively prevent a decrease in strength of the piercing portion of each through hole. In particular, since the cylindrical portion 11 and the hanging rod 21 of the support rod 10 are usually made of a glass material such as quartz glass, the effect of preventing the strength reduction is significant.
[0025]
3 to 4 show another example of the gripping state between the lower end of the support rod and the suspension rod on the optical fiber preform side in the method of the present invention.
This case is basically the same as the case of FIG. 1 to FIG. 2, but here, three locking pins 30 </ b> A to 30 </ b> C are prepared, and correspondingly, the support rod 10 is provided. In the cylindrical portion 11 and the suspension rod 21 on the optical fiber preform side, through holes 12A to 12C and 32A to 32C are provided from three different directions (from three different directions of about 60 °).
[0026]
These three locking pins 30A to 30C are used in the same manner as in the case of FIGS. 1 and 2 above, and thereby it is possible to more effectively prevent fluctuation during rotation of the optical fiber preform. It becomes.
[0027]
<Example I>
In the gripping state using the two locking pins shown in FIGS. 1 to 2 (the outer diameter of the suspension rod on the optical fiber preform side = 15 mm, the cylindrical portion of the support rod and the optical fiber preform side) The soot deposit is obtained by depositing the soot so as to have a relative refractive index difference of Δ = 2.5% between the core and the clad by the VAD method by the distance L between the vertical through-holes of the hanging rod. After that, dehydration and transparency were performed to obtain an optical fiber preform as a core material.
[0028]
At this time, the core non-circularity of the core material remains substantially circular from the start of deposition (deposition) to the end of deposition (the final soot outer diameter and soot length are about 120 mm and 800 mm, respectively). The non-circularity of the base material after ligation was only 0.1%. Here, the non-circularity of 0.1% means a state where the difference between the maximum diameter and the minimum diameter of the core diameter is 0.1%. The polarization mode dispersion (PMD) of the optical fiber obtained using this core material was 0.2 Ps / Km ^1/2 . Although this depends on the transmission method, the level of PMD normally required is 0.25 to 0.30 Ps / Km ^1/2 or less, and it can be seen that this is in a good range. Furthermore, since the refractive index distribution state of the core and the core / cladding magnification hardly change in the longitudinal direction, all the characteristics such as bending loss, chromatic dispersion, and dispersion slope at both ends of the optical fiber were satisfactory.
[0029]
<Example II>
3 to 4 in the holding state (the outer diameter of the suspension rod on the optical fiber preform side = 15 mm, the cylindrical portion of the support rod and the optical fiber preform side) The soot deposit is obtained by depositing the soot so as to have a relative refractive index difference of Δ = 2.5% between the core and the clad by the VAD method by the distance L between the vertical through-holes of the hanging rod. After that, dehydration and transparency were performed to obtain an optical fiber preform as a core material.
[0030]
At this time, the core non-circularity of the core material remains substantially circular from the start of deposition (deposition) to the end of deposition (the final soot outer diameter and soot length are about 120 mm and 800 mm, respectively). The non-circularity of the base material after ligation was as extremely small as 0.08%. The PMD of the optical fiber obtained using this core material was 0.18 Ps / Km ^1/2 . This shows that the level of PMD is even better. Furthermore, since the refractive index distribution state of the core and the core / cladding magnification hardly change in the longitudinal direction, all the characteristics such as bending loss, chromatic dispersion, and dispersion slope at both ends of the optical fiber were satisfactory.
[0031]
<Example III>
In the gripping state using the two locking pins shown in FIGS. 1 to 2 (the outer diameter of the suspension rod on the optical fiber preform side = 15 mm, the cylindrical portion of the support rod and the optical fiber preform side) The soot deposit is obtained by depositing the soot so as to have a relative refractive index difference of Δ = 2.5% between the core and the clad by the VAD method by the distance L between the through-holes in the vertical direction of the suspension rod. After that, dehydration and transparency were performed to obtain an optical fiber preform as a core material.
[0032]
At this time, the core non-circularity of the core material was almost circular and no non-circular state was observed until the soot outer diameter was about 400 mm after the start of deposition. And soot lengths of about 120 mm and 800 mm, respectively, the non-circularity of the sintered base material was about 0.14%. From this, it is understood that the non-circularity is slightly deteriorated when the separation distance L between the through holes in the vertical direction is less than twice the outer diameter of the suspension rod on the optical fiber preform side (= 30 mm). . The PMD of the optical fiber obtained using this core material was 0.28 Ps / Km ^1/2 . It can be seen that this value is within the range of the normally required PMD described above. In addition, since the refractive index profile of the core and the core / cladding magnification are small in the longitudinal direction, all characteristics such as bending loss, chromatic dispersion, and dispersion slope at both ends of the optical fiber are almost satisfactory. .
[0033]
<Comparative Example I>
5 to 7 in the holding state (the outer diameter of the suspension rod on the optical fiber preform side = 15 mm), Δ = 2 between the core and the clad by the VAD method. Soot was deposited so as to have a relative refractive index difference of 0.5% to obtain a soot deposit, and thereafter, dehydration and transparency were performed to obtain an optical fiber preform as a core material.
[0034]
At this time, the core non-circularity of the core material was almost a perfect circle and no non-circular state was observed until the soot length was about 200 mm after the start of deposition. And soot lengths of about 120 mm and 800 mm, respectively, the non-circularity of the sintered base material was about 0.4%. Due to this large non-circularity, the PMD of the optical fiber obtained using this core material was 2.0 Ps / Km ^1/2 . As described above, it can be seen that the PMD level normally required is in the inappropriate range because it is 0.25 to 0.30 Ps / Km ^1/2 or less. Furthermore, since the refractive index distribution state of the core and the core / cladding magnification also changed in the longitudinal direction, characteristics such as bending loss, chromatic dispersion, and dispersion slope at both ends of the optical fiber could not be satisfied, resulting in defective parts.
[0035]
【The invention's effect】
As is clear from the above description, according to the method for manufacturing an optical fiber preform according to the present invention, the following excellent effects can be obtained.
[0036]
(1) First, in grasping (coupling) between the cylindrical portion at the lower end of the support rod on the manufacturing apparatus side and the suspension rod on the optical fiber preform side, a plurality of through holes and a plurality of latches provided on each member side Since it is based on pins, it can be done very easily and quickly, and good workability can be obtained.
[0037]
(2) Further, the through hole is not a special one like a screw hole, and may be a simple through hole, and the locking pin may be a simple rod-like body, which can be manufactured at low cost. In particular, the cylindrical portion of the support rod and the suspension rod on the optical fiber preform side are usually made of a glass material such as quartz glass.
[0038]
(3) Further, since it is only necessary to insert the locking pin into the through hole, it is natural that the gap between the cylindrical portion of the support rod and the suspension rod on the optical fiber preform side is filled. Is absolutely unnecessary.
[0039]
(4) Since the plurality of through holes provided on the respective member sides are bored from different directions, the lower end of the support rod with respect to the outer diameter of the suspension rod on the optical fiber preform side Even if the inner diameter of the cylindrical portion is large, a great anti-swaying effect on the suspension rod on the optical fiber preform side can be obtained. In particular, if the separation distance between the upper and lower through-holes is set to be twice or more the outer diameter of the hanging rod, a further excellent anti-sway effect can be obtained.
[0040]
(5) Of course, since the inner diameter of the cylindrical portion of the support rod is larger than the outer diameter of the suspension rod on the side of the optical fiber preform, the suspension on the side of the optical fiber preform is made after the heating process. Even if the rod is slightly deformed, it can be extracted without any problem.
[0041]
(6) Further, in the cylindrical portion at the lower end of the support rod and the suspension rod on the side of the optical fiber preform, each through hole is formed to be appropriately separated, so that the strength of the piercing portion of these members is also reduced. Can be prevented.
[Brief description of the drawings]
FIG. 1 is a partially longitudinal side view showing an example of a gripping state between a cylindrical portion at a lower end of a support rod and a suspension rod on an optical fiber preform side in a method for producing an optical fiber preform according to the present invention. .
FIG. 2 is a partial cross-sectional plan view of the gripping portion of FIG.
FIG. 3 is a partially longitudinal side view showing another example of the gripping state of the cylindrical portion at the lower end of the support rod and the suspension rod on the optical fiber preform side in the method for producing an optical fiber preform according to the present invention. It is.
4 is a partial cross-sectional plan view of the gripping portion of FIG. 3;
FIG. 5 is a partially longitudinal side view showing a conventional example of a gripping state of a cylindrical portion at the lower end of a support rod and a suspension rod on the side of the optical fiber preform in the method of manufacturing an optical fiber preform.
6 is an enlarged partial vertical side view of the gripping portion of FIG. 5;
7 is a partial cross-sectional plan view of the grip portion of FIG. 5. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Support rod 11 Cylindrical part 12A-12C of support rod Through-hole 21 Hanging rod 22A-22C by the side of optical fiber base material Through-hole 30A-30C Locking pin

Claims (2)

In the manufacturing method of the optical fiber preform in which the suspension rod on the optical fiber preform side is held at the lower end of the support rod for the optical fiber preform and the desired processing is performed,
A cylindrical portion is provided at the lower end of the supporting rod, and the cylindrical portion is penetrated for the locking pin at at least two positions that are appropriately spaced apart in the longitudinal direction and that have different radial directions. While the hole is provided, the upper end of the suspension rod on the optical fiber preform side inserted into the cylindrical portion of the support rod is also used for the lock pin at a position corresponding to the through hole for the lock pin. The through holes corresponding to each other on the cylindrical portion side and the suspension rod side are aligned and communicated, and a locking pin is inserted into each of the communicated through holes, and the optical fiber A method for manufacturing an optical fiber preform, wherein the preform is supported. 2. The light according to claim 1, wherein a space between the cylindrical portion of the support rod and each through hole of the suspension rod on the side of the optical fiber preform is at least twice the outer diameter of the suspension rod. Manufacturing method of fiber preform.

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